Conventionally, a bearing structure for a shaft is disclosed in, for example, Patent Document 1. In a bearing structure for a steering shaft including a steering shaft, a head pipe in which the steering shaft is inserted, and a bearing assembled between the steering shaft and the head pipe from an upper end side of the head pipe in a state in which an upper end portion of the steering shaft protrudes upward from an upper end of the head pipe, and configured to rotatably support the steering shaft, a double nut is threadedly coaxially fastened to the steering shaft from the upper end side of the head pipe to fasten and fix the bearing.